GSK-3 is a serine/threonine protein kinase. Two isoforms, i.e., α and β, which are encoded by distinct genes, have been identified (see Trends Biochem. Sci., 1991, Vol. 16, p. 177).
Both GSK-3 isoforms have a monomeric structure and are constitutively active in resting cells. GSK-3 was originally identified as a kinase that inhibits glycogen synthase by direct phosphorylation (see Eur. J. Biochem., 1980, Vol. 107, p. 519). Upon insulin activation, GSK-3 is inactivated, thereby allowing the activation of glycogen synthase and possibly other insulin-dependent events, such as glucose transport. Also, it has been known that GSK-3 activity is inactivated by other growth factors, such as IGF-1 or FGF, through signaling from receptor tyrosine kinases (see Biochem. J., UK, 1993, Vol. 294, p. 625; Biochem. J., UK, 1994, Vol. 303, p. 21; Biochem. J., UK, 1994, Vol. 303, p. 27).
GSK-3 inhibitors are useful in the treatment of disorders that are mediated by GSK-3 activity. In addition, inhibition of GSK-3 mimics the activation of growth factor signaling pathways and consequently GSK-3 inhibitors are useful in the treatment of diseases in which such pathways are inactive. Examples of diseases that can be treated with GSK-3 inhibitors are described below.
Type I diabetes is induced due to autoimmune destruction of β cells as pancreatic insulin production cells, resulting in deficiency of insulin. From this, it is necessary for a type I diabetic patient to routinely be administered insulin for maintaining life. However, in current insulin therapy, strict control of the blood glucose levels like the ability of normal β cells cannot be reproduced. Thus, type I diabetes is liable to induce diabetic complications such as retinopathy, nephropathy, neuropathy, great vessels hindrance or the like.
Type II diabetes is a multifactorial disease. Hyperglycemia is due to insulin resistance in the liver, skeletal muscle and lipid tissues coupled with inadequate or defective secretion of insulin from pancreatic islets. As a result, diabetic complications such as retinopathy, nephropathy, neuropathy, or great vessels hindrance are induced. Skeletal muscle is the major site for insulin-stimulated glucose uptake, and glucose removed from the circulation is either metabolized through glycolysis and the TCA cycle or stored as glycogen. Muscle glycogen deposition plays a very important role in glucose homeostasis, and Type II diabetic subjects have defective muscle glycogen storage. GSK-3, which is known to phosphorylate glycogen synthase, inhibits the accumulation of glycogen in peripheral tissues and lowers the reactivity of insulin, leading to an increase in blood level of glucose.
Recently, it has been reported that the expression of GSK-3 is stimulated in skeletal muscles of type II diabetic patients, and the GSK-3α activity and insulin in skeletal muscles are inversely correlated (see Diabetes, USA, 2000, Vol. 49, p. 263). Where GSK-3β and active GSK-3β variants (S9A, S9E) are overexpressed in HEK-293 cells, the GSK activity is inhibited (see Proc. Natl. Acad. Sci., USA, 1996, Vol. 93, p. 10228). In CHO cells in which insulin receptor and insulin receptor substrate 1 (IRS-1) are expressed, overexpression of GSK-3β brings about a decrease in the insulin activity (see 8: Proc. Natl. Acad. Sci., USA, 1997, Vol. 94, 9660). Recent research carried out using C57BL/6J mice with pyknic type diabetes has clearly shown that GSK-3 activity stimulation and insulin resistance are correlated to the progress of type II diabetes (see Diabetes, USA, 1999, Vol. 48, p. 1662).
Conventionally, lithium salts have been known to have inhibitory effects of GSK-3 activity (see Proc. Natl. Acad. Sci., USA, 1996, Vol. 93, p. 8455). It has been reported that the therapy using the lithium salts lowers glucose levels in both type I and II diabetic patients, thereby alleviating the severity of the disease (see Biol. Trace Elements Res., 1997, Vol. 60, p. 131). However, lithium salts have also been found to exhibit various side effects on molecular targets other than GSK-3.
From the findings described above, it can be concluded that GSK-3 inhibitors are effective therapeutics for the treatment of impaired glucose tolerance, type I diabetes, type II diabetes and complications thereof.
It is also suggested that GSK-3 is associated with progress of Alzheimer's disease. The characteristic pathological features of Alzheimer's disease are senile plaques due to agglomeration of amyloid beta (Aβ) peptide and the formation of intracellular neurofibrillary tangles, leading to a large quantity of neuronal cell death, resulting in dementia. It is believed that GSK-3 involves abnormal phosphorylation of tau protein, which causes a neurofibrillary change in the course of progress of Alzheimer's disease (see Acta Neuropathol., 2002, Vol. 103, p. 91). Also, it has been found that GSK-3 inhibitors can prevent neuronal cell death (see J. Neurochem., 2001, Vol. 77, p. 94). Therefore, it is believed that the application of GSK-3 inhibitors to Alzheimer's disease can delay the progress of the disease. To date, therapeutic agents for Alzheimer's disease have mainly been used in conjunction with allopathy (see Expert Opin. Pharmacother., 1999, Vol. 1, p. 121). However, there is no known pharmaceutical agent that is effective in preventing neuronal cell death and delaying the onset or progress of Alzheimer's disease. These findings imply that GSK-3 inhibitors are effective pharmaceutical agents in alleviating the severity of Alzheimer's dementia.
There is a report that GSK-3 inhibitors suppress neuronal cell death, specifically, neuronal cell death due to overexcitement through glutamic acid (see Proc. Natl. Acad. Sci., USA, 1998, Vol. 95, p. 2642; J. Neurochem., 2001, Vol. 77, p. 94). This suggests that GSK-3 inhibitors are possibly useful in the treatment of bipolar affective disorder such as manic depressive psychosis, epilepsy or other degenerative brain injury or neurodegenerative diseases. Examples of the neurodegenerative disease include in addition to the Alzheimer's disease, AIDS encephalopathy, Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, Pick's disease, progressive supranuclear palsy and so on. Also, overexcitement through glutamic acid is presumably a principal cause of brain dysfunction in stroke, including cerebral infarction, intracerebral hemorrhage and subarachnoid hemorrhage, traumatic cerebrospinal injury, bacteria/virus infectious disease, and GSK-3 inhibitors are expected to be effectively used in the treatment of these diseases. All of such diseases accompany neuronal death. Currently, no therapeutic agents for effectively suppressing neuronal death are available. Therefore, GSK-3 inhibitors are believed to become potentially effective pharmaceutical agents for the treatment of various kinds of neurodegenerative diseases, dipolar affective disorders (manic-depressive psychosis), epilepsy, stroke, traumatic cerebrospinal injury, and the like.
Several in vitro research results have led to a report that Wint10B potently suppresses the differentiation of preadipocytes to mature fat cells (see Science, 2000, Vol. 289, p. 950). GSK-3 specific inhibitors mimic Wint10B signaling in preadipocytes, that is, GSK-3 specific inhibitors stabilize free β-catenin in cytoplasm and suppress the induction of C/EBPα and PPARγ, thereby suppressing the formation of fat (see J. Biol. Chem, 2002, Vol. 277, p. 30998). GSK-3 inhibitors are therefore potentially useful as effective pharmaceutical compositions for treating obesity.
Also, β-catenin has been known to be a GSK-3 substrate in vivo. After phosphorylation by GSK-3, β-catenin is subjected to proteosome-dependent degradation (see EMBO J., 1998, Vol. 17, p. 1371). Meanwhile, transient β-catenin stabilization may lead to increase hair development (see Cell, 1998, Vol. 95, p. 605). Consequently, GSK-3 inhibitors are believed to be a useful medicament for the treatment of alopecia.
Further, research into GSK-3β knock out mouse-derived fibroblasts implies that GSK-3β regulates the activity of transcription factor NFκB to be at a positive level (see Nature, 2000, Vol. 406, p. 86). NFκB is in charge of cell responsiveness to numerous inflammatory stimuli. Thus, GSK-3 inhibitors may have beneficial effects in the treatment of inflammatory diseases such as arthrosis deformans, rheumatism, atopic dermatitis, psoriasis, ulcerative colitis, Crohn's Disease, sepsis, or systemic inflammatory response syndrome, by adjusting the NFκB activity to be at a negative level.
A transcription factor NF-AT is dephosphorylated by calcineurine and increases immunosuppressive response (see Science, 1997, Vol. 275, p. 1930). Conversely, GSK-3 phosphorylates NF-AT and transports the same from nuclei, thereby suppressing the expression of initial immune response gene. Thus, GSK-3 inhibitors could be useful to immunity activation for cancer immunotherapy.
Examples of materials that have conventionally been known to have GSK-3 inhibiting activity include hymenialdisine derivatives (see Chemistry & Biology, 2000, Vol. 7, p. 51, and WO01/41768 pamphlet), maleiimide derivatives (see Chemistry & Biology, 2000, Vol. 7, p. 793), paullone derivatives (see Eur. J. Biochem., 2000, Vol. 267, p. 5983 and WO01/60374 Pamphlet), purine derivatives (see WO98/16528 Pamphlet), pyrimidine and pyridine derivatives (see WO99/65897 Pamphlet), hydroxyflavone derivatives (see WO00/17184 Pamphlet), pyrimidone derivatives (see WO00/18758, WO01/70683, WO01/70729, WO01/70728, WO01/70727, WO01/70726, and WO01/70725 Pamphlets), pyrrole-2,5-dione derivatives (see WO00/21927 and WO01/74771 Pamphlets), diamino-1,2,4-triazolecarboxylic acid derivatives (see WO01/09106 Pamphlet), pyrazine derivatives (see WO01/44206 Pamphlet), bicyclic inhibitor (see WO01/44246 Pamphlet), indirubine derivatives (see WO01/37819 Pamphlet), carboxamide derivatives (see WO01/42224 Pamphlet), peptide inhibitors (see WO01/49709 Pamphlet), 2,4-diaminothiazole derivatives (see WO01/56567 Pamphlet), thiadiazolidindione derivatives (see WO01/85685 Pamphlet), aromatic amide derivatives (see WO01/81345 Pamphlet), and so on.
Also, the claims of WO02/085909 Pamphlet show a wide variety of compounds including pyrrolopyrimidine derivatives. However, bicyclic pyrrolopyrimidine derivatives actually synthesized are those having cyano groups at the 7-position of pyrrolopyrimidine ring and limited variety of substituents at other substitutable positions. In addition, while it discloses a method for assaying inhibitory activity of GSK-3 etc., it is silent about which compounds have such activities.